Safety cutoff for power-operated hand tools



im i5, m, E F,SHEEHAN ETA; f 2,409,397

SAFETY CUTOFF FOR POWER OPERATED' HAND TOOLS Filed Oct. 13, 1943 2Sheets-Sheet l A .CSOURCE Oct. 15, 1946.

v E. F; sHEr-:HAN ETAL SAFETY CUTOFF FOR POWER OPERATED HAND TOOLS 2sheets-sheet 2 Filed oci. 15, 1943 Patented Oct. 15, 1946 UNITEDs'rrxr-ls PATENT ortica sAFE'rvoUfronFroR POWER-,onimusha HAND 'rooLsEdward Lstechen and George-v. Hunt, n rmladelpma;, ra. 4

Application iOotobcr 13, 19313,;Scriall No. 5106398.43

' l Objects :of `the :present ;-iny ention .are first, '.to y-protectworkmen and equipment-rand sub-surface structures when 'pow-er :driven4manually guided tools are -used for cutting, drilling, `:breaking or`working on :relatively nonaelectrically icon-ducting material in orunder orin :contact -Withwhichirellyatively high electrically conducting.material may be embedded, for-'example when such tools 'work Aonasphalt or other like stnee'tinavement inwhich, .or .in the foundationof which, or "under which high tension 4metal-lic sheath :cables:irl-.pipes carrying water; gas, steam Aor `other fluids., :or telephoneand other conduits are usually laid orlocated; second, to automaticallyoff .the power ,and stop the opera-tion of :the tool as soon :aait 1-has `penetrated the "layer `of :relatively mon-electrically conducting`zanraterial ,and contacted an underlying Yor :adjoining layerv Vof:relatively high conducting material; third, Ito automatically cutoffthe power and 'therefore to stop .the :tool immediately it contacts withrelatively high .electrically :conducting material, for lexample lthemetal ,sheath of ,a :cable and before sit Acontacts with the hightension conductors contained and insulated from fthe 'metallic sheath;fourth, to provide simple, reliable and efficient ,apparatus for:accomplishing the objects indicated :as well as the objects tanti:results :hereinafter rset forth or :appearing: ,fth :lto `loros/tide`for 'workinga power driven Vhand :guided tool on' an intended Ymaterial :in the way and for automatically stopping it as soon asii-tcontacts with and `befnre fit penetrates another material 'which itmight damage :or which :might he highly :charged with Aa :hazardousmedium-and cause injury to tele..

phone, water, electric :power or other :systems or injury to `theoperator :or `damage to fthe tool; sixth, to provide for automatically,stopping :a pneumatic :hand tool Working lon n :street lpavement,building floor, -or the like, in the event f that fand as soon as itcontacts lwith and -betore it penetrates an object such :as is :likelyto loe buried in or under .the pavement, Vfloor or "the like, :and whichmight ,be damaged by the tool,

or itself cause injury to the tool `.orto the 'operator; seventh, toprovide a supervisory vv.electric circuit for shutting dow-nthe toolupon :occurrence of the'conditions under .which :it :desired to Istopthe tool; zeig-nth, kto ,provide 'for shut-down of the tool incase of.failure of electric ,power to the supervisory electr-ic circui-t;ninth, to provid-e a visual Lsignal to Aindicate :failure of electricpower to the supervisory electric circuit; tenth, to `provide `a:seal-in .provision in the Vsupervisory electric circuit to causecompletion of the tool 3 .oni-ms; (ol. 121-35.)

stopping operation lonce ,theshutt-lng downlacton of the supervisorycircuit .is initiated -by .elven momentary occurrence of the `conditionunder which tit is desired wto stop the --toolg and-eleventh, toprov-ide an :audi-ble signal ,to .indicate 1that lthe tool has been shutdownley contact with mate.- rial which is relatively a goed :electric.conducton Other` objects of the invention wil-l Yappear.from :theYfollowing description .et the rend of which-the invention will `-beclaimed. Y i

The invention also icomprises ,the improvements to loe ,presentlydescribed and ,finally clair-ned I-n the ,following descriptionreference will vbe made .to the accompanying draw-ings forming parthereof :andin which, l l

Figure .l is v-a diagrammatic :View .illustrating :all alternatingYcurrent loper-ated ,safety cut-,off embodyinggfeatures .of vtheinvention ,and ,showing or indicating the Lposition of the lparts of.the valye mechanism when the ,tool is cut oil from the 4sour-ee ofpower. i

Figure vf2 is asimilar view yshowing ,the position of the jpants whenthe tool -isiconnected with :the source-of power; 1and Figure 3 isa viewsimilar `to Eigure l .and ill-us- Vtra'ting the employment -of lafdirect- 1,cu-rnent .circuit ,and omitting certain rteatures ,showninFigS. l iand2.

Referring to the drawings, ,I indicates a .han-diguided Ypovweroperatedtool, sneciicalvly a nnen'- mratic tool. `i'. indicates ,arsourcevof`power f orfop erating the tool. .3 is :a vsalve housing in cludes avalve mechanismhav-ng a `port-A. .tor ,admitting `air under lprensure-to the tool -by way of the hose The valve .mechanismalso includes -aport r6 `for exhausting :air under Vpressure from the tool by of thepipe .5 ,to the :atmosphere at I. The valves of the -valve mechanism.are operated ,by `the pivotal .arm B which is shown in FigureZ in.position for operating the tool under power, .and .in Figure 1 ,it is`shown imposition .for cutting .oli the supply of .fluid under pressurefrom the source and for exhausting :from the .tool and line 5 totheatmosphere so ,that ,thetoo'l stops quickly. .The pi-votalhand-le 3 isconnected by a link withthe .arm S the spring I9 opr .crates to normallyput .and ,hold the valves the position shown in Figure l inwhichnosition the tool l `is Vat rest. ll is a ,pivotal latch normallyTpositioned by .the spring l2, as .shown in Figure 1 `in Vwhich .positionit disengagesthe handle` 9 at VI3 .whenthe power is out .off from thetool and. it engages the handle ..9 .at lI3 when the tool is operating.under power, The 'latch ,l .l `is oon'tnol-lecl by .the solenoid ,L4.which when energized causer 3 the latch to hold the handle 9 inposition, thereby permitting the tool to operate under power. The handle9 may be shifted to latched position manually or otherwise. The solenoidI4 is shown as included across the leads I5 and I6 of the A. C. source.I'I is a sensitive fast-acting two pole double-throw relay whichnormally closes the line I6 so that the latch II is normally heldagainst the force of its spring I2 in position for engaging the handle 9and permitting the tool I to operate in the ordinary and usual manner.If the position of the two pole double-throw relay be changed toward theright in Figure 1, lthe circuit through the solenoid will be broken, thespring I2 will release the latch and the tool will stop. The coil I9serves to shift the position of the two pole double-throw relay IIappropriately for stopping the tool. There is a lead 20 from one side ofthe secondary of the transformer I8 through the coil I9 to a relativelylow resistance ground at 2I.v Two leads 22 and 23 extend from thesecondary of the transformer to the tool I where they may be regarded asconnected together and to the tool I, and in the lead 23 there is asignal lamp 24. At this point'in the description it may be said that thetool I is for the purposes of description, assumed to be a pneumatictool and is intended to operate upon or work on material a, ofrelatively low electrical conductivity, for example the asphalt pavementof a street. In the pavement there is likely to be embedded material ofrelatively high electrical conductivity, such for example as a hightension lead covered cable b grounded for example at c. It must, ofcourse, be understood that the foregoing explanation is given by way ofdescription and not by way of limitation, for example, lthe tool may beoperated otherwise than by air, and 'che material b, so long as it is ofrelatively high electrical conductivity, may be a telephone cable, pipeor the like. and the material a may be the earth beneath the pavement.Riesuming the description and assuming the tool to be working in or onthe material a of relatively low electrical conductivity, any groundcircuit that may exist is of too high resistance to permit the coil I9to be energized sufficiently to throw the relay I1. However, if the toolcontacts the material b of relatively high conductivity, the groundcircuit between 2| and c is of relatively low resistance and is of goodconductivity and permits of the energization of the coil I9 sufficientlyto throw the relay II and stop the tool.

Because the contact of the tool I with the material b, may be momentaryor of chattering nature, a sealing-in circuit is provided to prevent thefast-acting relay I'I being deenergized and restored to its normalposition before the latchholding solenoid I4 can function to release thelatch II and permit the valve to assume the cut-off position. Thissealing-in circuit comprises the lead 25 from one side of the secondarycircuit of the transformer to the handle 9 and thence through the lead26, the armature of the relay I'I, the coil I 9, and the conductor 20,back to the other side of the secondary circuit of the transformer. Withthe valve mechanism in the tool-operative position illustrated in Fig.2, the relay II, when energized and thrown to the right,

will remain in that position because the coil I9 u will remain energizedthrough the sealing-in circuit regardless of any opening or chatteringof the ground circuit through the tool I and material b. This will allowany time lag which may be required for the solenoid I4 to release latchII 4 and permit the handle 9 to take up the toolstoppng position shownin Fig. 1. The parts are so constructed that when the handle 9 has movedfar enough to release engagement with the lead 26, the latch Il will notbe able to reengage the latch pin I3.

There is also a lead 21 through the alarm 28 to the contact at therother side of the handle 9 so that when the valve is in position forstopping the tool the circuit is closed through the signal 28 whichindicates that the power is cut off from the tool. Obviously, ifdesired, the sealing-in circuit may be omitted and it is, therefore, notshown in Figure 3. In the latter figure there is a D. C. source but thecircuits and translating devices are, as has been described, inconnection with Figures 1 and 2. In this case, however, there is a lead29 from one side of the circuit which branches to and through the coilI9' Ito ground at 2 I, and through signal 28 and lead 29 through thetwo-pole double-throw relay Il back to the line. The operation of theapparatus shown in Figure 3 is as above described in connection withFigures 1 and 2 except as indicated above. In both Figures 1 and 3, 30is a blocking switch which is, of course, normally closed.

The operation of the apparatus of Figs. 1 and 2 may be summarized asfollows: Under normal conditions the hand tool, driven pneumatically orby other power, with the valve mechanism in the Iposition illustrated inFig. 2, is operated in the usual manner to disintegrate pavement orother material of relatively high electric resistance a. If, however,the Pneumatic ltool in its normal operation makes contact withunderground water pipes, conduits or the like, b, an electric circuit iscompleted from one terminal of the secondary winding of transformer I8by Way of conductor 22 through the tool I, conducting medium b, groundsc and 2|, coil I9, and conductor 20 to the other terminal of saidwinding. Flow of current in this circuit energizes coil I9, throwingrelay I1 to the right and energizing the sealing-in circuit to hold Itherelay in this position despite any chattering of the tool. Thisenergizing of the relay II opens the .circuit from the electric sourceIto the solenoid I4, thereby permitting the spring I2 to release thelatch II The spring I0 is then free to move the arm 8 and handle 9 tothe tool-stopping position shown in Fig. 1, moving the valve to cut offthe air supply and permit the line 5 to exhaust to the atmosphere at 1.This movement of the handle 9 to the position shown in Fig. 1 connectsthe audible signal 28 to the secondary winding of transformer I8 todirect attention to the occurrence of valve operation. The visual signal24 is connected to the transformer I8 and when energized indicates (1)that the supervisory electric circuit is energized, and (2) that theflexible electric conductor 22 to the tool is unbroken, it being readilyunderstood that this conductor is subjected to considerable flexure andpossible abuse and is therefore likely to break. The apparatus is resetfor operation of the tool by merely moving the handle 9 upwardly intothe position shown in Fig. 2, the latch II automatically engaging withthe pin I3. It is obvious, of course, that should failure of theelectric source occur, solenoid I4 will be deenergized and the tool willshut down. The supervisory electric circuit of the device shown in Fig.3 operates in a similar manner from a direct current source, but withoutthe sealing-in feature.

It may be remarked that as a matter of convenience certain of thedescribed Working parts may be assembled in a portable housing or case,for example, the valve mechanism, indicated at 3, may be arranged in thecase with the handle 9 projecting to theoutside, and the blocking switch3@ may be similarly arranged. The signal lamp 24 may be displayed at theoutside of the case, and the relay Il may be arranged inside of thecase, and, if desirable, there may be arranged in the case as a D. C.source a storage battery, and the alarm 23 may also'be arranged in thecase and in that way the invention is applied to street paving and likeWork in a convenient manner.

It will be obvious to those skilled in the art that modifications may bemade in details of construction and arrangement and application inrespect to the apparatus chosen for illustration and above describedwithout departing from the spirit of the invention, which is thereforenot limited as to such matters or as to matters of mere form orotherwise than .the appended claims may require.

We claim:

l. A safety cut-off apparatus comprising in combination a power drivenhand tool, power cutoff means having yieldable means normally urgingsaid cut-off means to the cut-off position to stop the tool, a source ofelectric current, a rst electric circuit connected to said source andincluding an electro-mechanical detent constructed and arranged torestrain said yieldable means Y 6 i frommoving said cut-off means to thecut-o position'when said detent is energized by said electric currentand to release said yieldahle means lpermitting said cut-oi means toassume the cut-oil' position when the electric current .ta said detentis interrupted, a normally closed relay having its contacts in saidiirst circuit in series with said detent, a second electric circuitconnected to said source and including the operating coil of said relay,and means in said second circuit for energizing said relay operatingcoil responsive to the conditions under which it is desired tc stop thetool, whereby the .tool will be stoppedupon operation of the means forenergizing said relay operating coil and also upon the occurrence of anyother interruption of the current supply to said first circuit.

2. The invention set forth in claim 1 characterized in that the relayenergizing means is provided with a sealing-in circuit for holding saidrelay in tool stopping position when once in that position and untilmanually released.

3. The invention set forth in claim l characterized in that saidapparatus includes an electrically operated visual signal, said signalbeing connected in series with a part of said tool .to said electricsource, whereby the operator may be apprised that the circuit to the`tool is energized.

EDWARD F. SHEEHAN. GEORGE V. HUNT.

